The invention relates to a method for polymerizing alpha olefins by terminating a polymerization reaction, which is either liquid pool, gas phase or similar, and uses a high activity, magnesium supported, titanium halide/aluminum alkyl catalyst system.
Polymerization of alpha mono-olefin monomers by means of supported coordination catalyst systems can occur using catalyst systems which comprise (a) a procatalyst, (b) a cocatalyst and (c) a selectivity control agent, wherein (a) is a highly active solid composition which comprises magnesium, tetravalent titanium, halogen and one or more electron donors; (b) is an organoaluminum compound like aluminum alkyl; and (c) is an electron donor. Components (b) and (c) may be wholly or partly complexed with each other prior to being combined with the procatalyst.
Olefin polymerizations using magnesium supported titanium halide/aluminum alkyl catalyst systems are well known in the art. Recently, there has developed a need to terminate the olefin polymerization reaction rapidly and restart the reaction, obverting a long down time, and adding stability to the overall polymerization product.
It is known that the polymerization of monoolefins, particularly alpha olefins, such as propylene, in slurry or bulk phase polymerizations can be terminated by the addition of substances, such as alcohols, ketones, ethers, aldehydes, carboxylic acids, phenols, water, oxygen and carbon oxides, see U.S. Pat. Nos. 4,326,048 and 4,551,509. It is known that the polymerization of olefins, such as propylene or ethylene in gas phase processes can be terminated by the addition of carbon oxides.
In U.S. Pat. No. 4,326,048 carbon oxides were used to terminate a reversible gas phase alpha olefin polymerization reaction that utilized a titanium halide/aluminum alkyl catalyst system. The disclosed process involved the steps of (a) discontinuing catalyst addition by quenching reactor liquid flow and reactor off gas flow, (b) injecting an amount of carbon oxide sufficient to terminate the reaction, (c) discontinuing the recycle gas flow, (d) venting and flushing the polymerization reactor, (e) restarting the quench liquid, off gas, and recycle gas flows (f) injecting an amount of aluminum alkyl sufficient to initiate polymerization, and (g) resuming titanium halide addition.
This known process has several drawbacks. Under typical operating conditions for propylene polymerization, it is difficult to eliminate carbon oxides without a long down time in the polymerization system. It is expensive and difficult to remove the carbon oxide from the non-polymerized monomer because the volatility of the carbon oxide is similar to the volatility of the typical monomer used.
Another process for deactivating a polymerization reaction is taught in U.S. Pat. No. 4,551,509. In that patent, the catalyst system to be deactivated uses a procatalyst compound of a transition metal of groups IVa and VIa of the Periodic Table and an organometallic compound of a metal of groups I to III of the Periodic Table. Polyalkylene glycol is introduced in the reactor to deactivate the catalyst. In the patent, it is disclosed that the glycol component is only usable as a deactivation agent in a gas phase reaction, and that it does not provide any additional advantages, such as acting as a stabilizer, adding for the resulting polymer.
Another U.S. Pat. No. 3,965,083 discloses a method for terminating an alpha olefin polymerization using water as the reversible polymerization terminator. Water, like the polyalkylene glycol, does not additionally act as a stabilizer or antioxidant in the resultant polymer product.
U.K. Patent Application GB 2,094,319A discloses the use of compounds having at least one C--O bond to partially deactivate a Mg-supported olefin polymerization catalyst. Methyl p-toluate is disclosed. This is not a sterically hindered phenolic compound. Furthermore, it is not a high molecular weight phenolic compound.
A need has developed for a method which is capable of (1) reversible alpha olefin polymerization termination in gas phase, solvent slurry, liquid pool and bulk phase polymerization reactions and/or (2) acting as a stabilizer in the subsequently prepared polymer. It has now been discovered that certain polymerization termination components can act as reversible termination components in the polymerization process and as stabilizers in the final polymerized product.